In air conditioning appliances, water condenses on the walls of heat exchangers. This condensation water falls under gravity into tanks for recovering the condensate. Thereafter it must be removed in order to avoid overflows. Depending on the position of the tanks relative to the drain pipes, it may be necessary to provide pumps for raising the condensate. Such condensate-raising pumps are provided with control systems that put the pump automatically into operation whenever the level of liquid reaches a maximum predetermined level and that automatically stops operation of the pump when the level of the condensate liquid in the tank has gone back down to a minimum level.
Such control systems are connected to apparatuses for detecting the level of liquid in the tank and that issue a first signal when the level of the condensate reaches a maximum permitted level and a second signal when the level of the condensate reaches a minimum authorized level.
Level detector apparatuses are already known that include electrodes situated at different levels in the tank. Water allows a micro-current to pass from one electrode to another. The micro-current causes the pump to start or stop depending on the level of the condensate. That solution is compact, but unfortunately the quality of the water has an influence on the magnitudes of the micro-currents, and the presence of algae or of fat on the surface of the condensate can give rise to mis-operation.
To remedy those drawbacks, proposals have been made for liquid level detection apparatuses that include a float which is raised by the liquid, a magnet carried by the float, and at least two switches each having contacts sealed in an elongate glass capsule disposed in the vicinity of the path of said magnet and at respective different vertical heights, each of the switches causing an electrical circuit associated with said control to close when the switch is subjected to the magnetic field of the magnet. In known apparatuses, the capsules are disposed vertically or they are placed above the float.
The height of the detection apparatus is not less than the length of a capsule plus the difference between the minimum and maximum levels authorized for condensate in the tank. This height may be greater than 60 mm, particularly when a third capsule is provided connected to a device for detecting a safety level above the maximum level for putting the pump into operation. In certain types of air conditioner (ceiling mounted, wall mounted mini-split types) that require a shallow tank or the installation of a level sensor at the end of the condensate drain, this minimum possible height or possible size for the sensor housing can be unacceptable.
FR-A-2 683 316 shows one such device in which the capsules are disposed vertically in a guide tube for an annular float that caries an annular magnet.
EP-A-397 338 relates to apparatus for accurately measuring the level of liquid in a motor vehicle tank. That apparatus likewise includes an annular magnet carried by a cylindrical float which runs along a vertical wall placed close to superposed horizontal capsules. The object of that disposition is not to reduce the height of the apparatus but to increase the accuracy of measurement.